To an increasing extent, vehicle seats are provided with electric actuators in order to provide the vehicle passengers with ergonomic and comfortable seating in the vehicle and to make it possible for the passengers to adjust the respective seat position individually. The seat back is usually adjusted by way of stagger gears integrated in the seat back fittings.
In the electric seat back adjustments known previously, the adjusting gears are driven by way of electric motors that act on stagger gears. While, with electric positioning driver motors, the positioning of the seat takes place in a horizontally oriented plane and the course of torque and force changes continuously, a seat back adjustment on a vehicle seat is associated with a discontinuous course of torque. The upper torso weight of the person who is adjusting the seat back acts on the seat back to be adjusted and, depending on the degree of inclination of the seat back, creates a discontinuous course of torque for the driver motor on the drive end, especially when loaded. Depending on the adjustment position of the seat back, this makes itself felt as an irregular motor speed on the one hand, and, on the other, as an irregular set of noises produced by the driver motor.
With the selected installation position of the torsion element, this can be used on the one hand to compensate clearance within the stagger gears that adjust the seat back on both sides of the seat area; on the other hand, a preloading of the torsion element is possible by way of the downward motion of the seat back. If the seat back is now moved upward again in the direction of the vertical line, the torsion springxe2x80x94as an energy accumulatorxe2x80x94supports the upward motion of the seat back by the driver motor by way of its release of tension.
It is especially advantageous to design a transmission shaft that connects the two stagger gears as a hollow shaft that can enclose the torsion element. The greater the inner diameter that can be used for the hollow shaft, the stronger the torsion elements can be, as based on their diameter. The greater the diameter that can be used for the torsion bars used as torsion elements, for instance, the greater the supportive effect of the torsion elements are for the drive during the upward motion of the loaded seat back.
Using the solution proposed according to the invention, the clearance in the stagger gears that carry out the adjusting motion of the seat back can be compensated. This makes a continuous adjusting motion possible that proceeds uniformly and without jerking, without the seat back having to be relieved of its load. A square neck of the torsion element can be embedded with positive engagement in an abutment that encloses the square neck to safeguard the torsion bar, which extends through the transmission shaft between the stagger gears, against twisting. To save space, the torsion element can be installed inside a transmission shaft between the stagger gears designed as a hollow shaft; the configuration of the seat back fittings and the bearings of the stagger gears requires no modification; using the modular principle, identical parts can be used to the greatest extent.